The present invention relates to golf balls and, more particularly, to improved golf balls comprising multi-layer covers which, in several embodiments, are formed from particular combinations of ionomers and/or polyurethane based materials. In several of the embodiments, the cover layers are also relatively thin. And, in other embodiments of the present invention, the balls utilize a multi-layer core construction. The improved golf balls provide for enhanced distance and durability properties over conventional golf balls while at the same time offering enhanced xe2x80x9cfeelxe2x80x9d and spin characteristics generally associated with soft balata and balata-like covers of the prior art.
Traditional golf ball covers have been comprised of balata or blends of balata with elastomeric or plastic materials. The traditional balata covers are relatively soft and flexible. Upon impact, the soft balata covers compress against the surface of the club producing high spin. Consequently, the soft and flexible balata covers provide an experienced golfer with the ability to apply a spin to control the ball in flight in order to produce a draw or a fade, or a backspin which causes the ball to xe2x80x9cbitexe2x80x9d or stop abruptly on contact with the green. Moreover, the soft balata covers produce a soft xe2x80x9cfeelxe2x80x9d to the low handicap player. Such playability properties (workability, feel, etc.) are particularly important in short iron play with low swing speeds and are exploited significantly by relatively skilled players.
Despite all the benefits of balata, balata covered golf balls are easily cut and/or damaged if mis-hit. Golf balls produced with balata or balata-containing cover compositions therefore have a relatively short lifespan.
As a result of this negative property, balata and its synthetic substitutes, transpolyisoprene and transpolybutadiene, have been essentially replaced as the cover materials of choice by new cover materials comprising ionomeric resins.
Ionomeric resins are polymers containing interchain ionic bonding. As a result of their toughness, durability and flight characteristics, various ionomeric resins sold by E. I. DuPont de Nemours and Company under the trademark Surlyn(copyright) and more recently, by the Exxon Corporation (see U.S. Pat. No. 4,911,451) under the trademarks Escor(copyright) and Iotek(copyright), have become the materials of choice for the construction of golf ball covers over the traditional xe2x80x9cbalataxe2x80x9d (transpolyisoprene, natural or synthetic) rubbers. As stated, the softer balata covers, although exhibiting enhanced playability properties, lack the durability (cut and abrasion resistance, fatigue endurance, etc.) properties required for repetitive play.
Ionomeric resins are generally ionic copolymers of an olefin, such as ethylene, and a metal salt of an unsaturated carboxylic acid, such as acrylic acid, methacrylic acid, or maleic acid. Metal ions, such as sodium or zinc, are used to neutralize some portion of the acidic group in the copolymer resulting in a thermoplastic elastomer exhibiting enhanced properties, i.e. durability, etc., for golf ball cover construction over balata. However, some of the advantages gained in increased durability have been offset to some degree by the decreases produced in playability. This is because although the ionomeric resins are very durable, they tend to be very hard when utilized for golf ball cover construction, and thus lack the degree of softness required to impart the spin necessary to control the ball in flight. Since the ionomeric resins are harder than balata, the ionomeric resin covers do not compress as much against the face of the club upon impact, thereby producing less spin. In addition, the harder and more durable ionomeric resins lack the xe2x80x9cfeelxe2x80x9d characteristic associated with the softer balata related covers.
As a result, there are currently more than fifty (50) commercial grades of ionomers available both from DuPont and Exxon, with a wide range of properties which vary according to the type and amount of metal cations, molecular weight, composition of the base resin (i.e., relative content of ethylene and methacrylic and/or acrylic acid groups) and additive ingredients such as reinforcement agents, etc. However, a great deal of research continues in order to develop a golf ball cover composition exhibiting not only the improved impact resistance and carrying distance properties produced by the xe2x80x9chardxe2x80x9d ionomeric resins, but also the playability (i.e., xe2x80x9cspinxe2x80x9d, xe2x80x9cfeelxe2x80x9d, etc.) characteristics previously associated with the xe2x80x9csoftxe2x80x9d balata covers, properties which are still desired by the more skilled golfer.
Consequently, a number of two-piece (a solid resilient center or core with a molded cover) and three-piece (a liquid or solid center, elastomeric winding about the center, and a molded cover) golf balls have been produced by the present inventor and others to address these needs. The different types of materials utilized to formulate the cores, covers, etc. of these balls dramatically alter the balls"" overall characteristics.
In addition, multi-layered covers containing one or more ionomer resins have also been formulated in an attempt to produce a golf ball having the overall distance, playability and durability characteristics desired. For example, this was addressed by Spalding Sports Worldwide, Inc., the assignee of the present invention, in U.S. Pat. No. 4,431,193 where a multi-layered, regular sized, golf ball is disclosed.
In the ""193 patent, a multi-layer golf ball is produced by initially molding a first cover layer on a spherical core and then adding a second layer. The first layer is comprised of a hard, high flexural modulus resinous material such as type 1605 Surlyn(copyright) (now designated Surlyn(copyright) 8940). Type 1605 Surlyn(copyright) (Surlyn(copyright) 8940) is a sodium ion based low acid (less than or equal to 15 weight percent methacrylic acid) ionomer resin having a flexural modulus of about 51,000 psi. An outer layer of a comparatively soft, low flexural modulus resinous material such as type 1855 Surlyn(copyright) (now designated Surlyn(copyright) 9020) is molded over the inner cover layer. Type 1855 Surlyn(copyright) (Surlyn(copyright) 9020) is a zinc ion based low acid (10 weight percent methacrylic acid) ionomer resin having a flexural modulus of about 14,000 psi.
The ""193 patent teaches that the hard, high flexural modulus resin which comprises the first layer provides for a gain in coefficient of restitution over the coefficient of restitution of the core. The increase in the coefficient of restitution provides a ball which serves to attain or approach the maximum initial velocity limit of 255 feet per second as provided by the United States Golf Association (U.S.G.A.) rules. The relatively soft, low flexural modulus outer layer provides essentially no gain in the coefficient of restitution but provides for the advantageous xe2x80x9cfeelxe2x80x9d and playing characteristics of a balata covered golf ball.
Unfortunately, however, while a ball of the ""193 patent does exhibit enhanced playability characteristics with improved distance (i.e. enhanced C.O.R. values) over a number of other then known multi-layered balls, the ball suffers from poor cut resistance and relatively short distance (i.e. lower C.O.R. values) when compared to two-piece, single cover layer balls commercially available today. These undesirable properties make the ball produced in accordance with the ""193 patent unacceptable by today""s standards.
The present invention is directed to new multi-layer golf ball compositions which provide for enhanced coefficient of restitution (i.e, enhanced resilience or carrying distance) and/or durability properties when compared to the multi-layer balls found in the prior art, as well as improved outer cover layer softness and durability. As such, the playability characteristics (i.e., xe2x80x9cfeelxe2x80x9d, xe2x80x9cclickxe2x80x9d, xe2x80x9cspinxe2x80x9d, etc.) are not diminished.
These and other objects and features of the invention will be apparent from the following summary and description of the invention, the drawings and from the claims.
The present invention is directed to improved multi-layer golf ball cover compositions and the resulting multi-layer golf balls produced using the improved compositions. The present invention is also directed to improved multi-layer golf balls having particular properties and characteristics.
In a first aspect, the present invention provides a golf ball comprising a multi-layer core assembly that includes a center core component and a core layer disposed about the center core component. The golf ball further comprises a multi-layer cover assembly including an inner cover layer disposed on the core layer and an outer cover layer disposed on the inner cover layer. The golf ball is characterized by one or both of the inner cover layer and outer cover layer comprising a blend of less than 50 percent of a high acid ionomer and greater than 50 percent of a low acid ionomer.
In yet another aspect, the present invention provides a golf ball comprising a multi-layer core assembly having a center core component and a core layer disposed about the center core component. The golf ball further includes a multi-layer cover assembly including an inner cover layer disposed about the core assembly and an outer cover layer disposed on the inner cover layer. One or both of the inner cover layer and outer cover layer comprise a thermoplastic polyurethane.
In yet another aspect, the present invention provides a golf ball that includes a multi-layer core assembly comprising a center core component and a core layer disposed on the center core component. The golf ball further includes a multi-layer cover assembly formed about the multi-layer core assembly. The multi-layer cover assembly comprises an inner cover layer disposed on the core layer and an outer cover layer disposed on the inner cover layer. The multi-layer core assembly exhibits a PGA compression of less than 85.